The present invention relates to a bobbin structure. More specifically, the present invention relates to a bobbin structure that prevents damage due to oscillations and shocks, and to rotary transformers and inductors employing same.
The present application is based in Japanese Patent Application No. 2002-135367, which was filed on May 10, 2002, and which is incorporated herein by reference, in its entirety, for all purposes.
In the past, magnetic cores, constructed from magnetic materials such as ferrite and silicon steel, and bobbins, where windings are wound, have been employed in constructing transformers and inductors. An example of the bobbin structure is found in a rotary transformer, which is employed for signal input/output for such well-known devices as resolvers, synchros, etc. One specific example is disclosed in the Japanese Unexamined Patent Application Publication S63-318725. As shown in FIG. 9, the rotary transformer includes a ring-shaped case 1, which encloses a resolver 2 and a rotor 3. Resolver stator 5, having resolver stator winding 4, and stator transformer 7, having stator transformer winding 6, respectively, are provided in parallel on the side of case 1. Bobbin 71 is disposed in the stator transformer 7; stator transformer winding 6 is wound on the bobbin 71. In contrast, the rotor winding 12 is directly wound on the rotor transformer 13. Stator transformer winding 6 and resolver stator winding 4 are led to the outside of case 1 via socket 71d having projecting pins 81 and directly by lead line 82, respectively.
On the rotating shaft (not shown), which is provided inside case 1 so that it rotates freely, is provided a resolver rotor 11, having a resolver rotor winding 10, and a rotor transformer 13, having a rotor transformer winding 12, respectively, disposed in a parallel manner. The electric current supply and input/output of the signal to the resolver 2 are carried out via the rotary transformer 3. This stator transformer 7 is fit to the case 1 side with a fastening ring 8, e.g., a “C” ring.
FIG. 10 is an exploded view illustrating the structure of the stator transformer 7 having stator transformer winding 6. Stator transformer 7 includes core portions 70 and 72 between which bobbin 71 is disposed, which core portions are constructed from, for example, a nickel-iron alloy (Permalloy), an iron-cobalt alloy or silicon steel, or ferrite. The external diameter of stator transformer 7 is ΦC. Through holes, i.e., bores, generally denoted 80 accommodating rotor transformers (not shown) are formed in each of core portions 70 and 72. Core portion 72 includes a bottom collar 72c in which a through hole 80, where a rotor transformer (not shown) resides, is formed at its center. Furthermore, a cylindrical standing wall 72a is formed on the bottom 72c; the edge 72b of standing wall 72a is covered by the core portion 70. Notch 72d is formed in the standing wall 72a, which notch is sized to accept a socket 71d, which protrudes from the bobbin 71.
On opposite sides of the spool 71c of the bobbin 71, where a winding (not shown) is wound, collars 71a and 71b are formed. By making socket 71d, having projecting pins 81 formed on one of the collars 71b, which coincides with the notch 72d of the core 72, the bobbin is positioned in the core portion 72, and then collar 71a of the bobbin 71 is covered with the core portion 70. The external diameter ΦA of the collars 71a and 72b of the bobbin 71 is slightly smaller than the internal diameter ΦB of the standing wall 72a of the core portion 72.
Core portions 71 and 72 are joined or fused to one another during assembly with well-known adhesives. In other words, an assembly method is employed in which, after positioning the bobbin 71 in the core portion 72, bobbin 71 is fixed to the core portion 72 by dipping it in and/or coating it with well-known adhesives or resin.
In contrast, the rotor transformer 13, having a rotor transformer winding 12, does not employ a bobbin; the rotor transformer winding 12 is wound directly on the rotor transformer 13. By dipping the rotor transformer 13 in well-known adhesives or resin, the rotor transformer winding 12 is fixed to the rotor transformer 13. This construction is dictated by the fact that the rotor transformer 13 normally rotates at high speed. If a bobbin were employed, the bobbin could be separated from the adhesive or resin, or could otherwise be damaged due to the oscillations or inertial force generated during acceleration or deceleration of the rotor transformer.
In addition, a variety of inductors fabricated using a well-known pot-shaped core employ a similar bobbin. The external diameter ΦA of the collars 71a and 71b of the bobbin 71 is formed so that it is slightly smaller than the internal diameter of the standing wall of the pot-shaped core. Thus, after positioning the bobbin 71 in the pot-shaped core, bobbin 71 is fixed to the pot-shaped core by dipping the assembly in well-known adhesives or resin.
However, with the aforementioned rotary transformer and pot-shaped core, the following problems have been noted. First, in the case where the bobbin 71 is fixed to the core, after the bobbin 71 is positioned in the core, by dipping in well-known adhesives or resin, the number of additional process steps related to adhering and drying are increased, i.e., there are many processes employed to control the amount of adhesives, the adhering area, the drying temperature and the drying time, etc. Therefore, it is difficult to assure the reliability of the finished product. In particular with the respect to the rotary transformer, there are defects such as misalignment between the revolving center of the core and bobbin and, as a result, the precision and reliability of the rotary transformer may be reduced due to the changes in the inertial force during revolution, etc.
Moreover, in the case of rotor transformer 13, the rotor transformer winding 12 is fixed to the rotor transformer 13 by dipping in well-known adhesives or resin even when the rotor transformer will be used for a device with a low revolution speed, e.g., a torque detector. As with the stator transformer 7, the number of process steps related to adhering and drying are increased, i.e., the many process steps require numerous control parameters such as the amount of adhesives, the adhering area, the drying temperature, and the drying time. Thus, it is difficult to assure the reliability of the finished rotor transformer.
What is needed is bobbin having a structure resistant to damage due to oscillation and shocks, making the bobbin suitable for use in transformers and inductors. Moreover, what is needed is a bobbin having a mechanism insuring the precise alignment of the bobbin with respect to a surrounding core.